Force responsive power tool

ABSTRACT

A controller coupled to a motion actuator responsively varies a speed of the motion actuator and an operating speed of a working surface within the range of an initial speed and a max speed and responds to a derived force that represents an amount of force an operator applies between a workpiece and the working surface. The controller, under both acceleration and deceleration, allows the operator with an applied force to manageably change simultaneously both a rate of work on the workpiece and the operating speed of the working surface according to a sensitivity profile expressing a relationship between the derived amount of force and the operating speed of the working surface. A tool for operating on the workpiece includes the motion actuator coupled to the working surface to engage the workpiece.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of provisional application61/802,260, filed Mar. 15, 2013, entitled “LOAD-RESPONSIVE SPEED CONTROLSYSTEM FOR POWER TOOL MOTORS” and is hereby incorporated within byreference.

BACKGROUND

When skilled machinists or artisans are making fine objects requiringmeticulousness or perfectionism, they often find conventional powertools to be of limited use due to safety and work quality concerns. Theyoften resort to using less efficient finishing tools that provide themwith more control and finesse in the creation of fine-craftedworkpieces.

BRIEF DESCRIPTION OF THE DRAWINGS

The description is better understood with reference to the followingdrawings. The elements of the drawings are not necessarily to scalerelative to each other. Rather, emphasis has instead been placed uponclearly illustrating the description examples. Furthermore, likereference numerals designate corresponding similar parts through theseveral views.

FIG. 1 is a block diagram of an example tool which an operator may useto fashion a workpiece incorporating the concepts described herein;

FIG. 2 is a block diagram of an example of a specific implementation ofa tool incorporating the concepts described herein;

FIG. 3 is an example of observed speed curve vs. derived force used inone example;

FIG. 4 is a drawing of an example motion actuator with example brakingmechanisms;

FIG. 5A is a graph showing several different types of examplesensitivity profiles which may be used in various examples;

FIG. 5B is a graph showing several example sensitivity profiles based ona common formula series which may be used in various examples;

FIG. 6A is a flowchart of an example method of controlling the speed ofa tool based on a derived force on a workpiece by an operator;

FIG. 6B is a flowchart of an example method of controlling the power ofa tool based on a derived force on a workpiece by an operator;

FIG. 6C is a graph showing a couple of example sensitivity profiles forpower supplied to a working surface vs. derived force;

FIG. 7 is a flowchart of an example method of creating a standardderived force signal based off a read parameter;

FIG. 8 is a table for a simplified example implementation of a controlsystem;

FIG. 9 is a graph showing several example sensitivity profiles withrespect to relative material removal rates;

FIG. 10 is a graph showing a couple example ratios of constant speed andforce responsive tool material removal rates; and

FIG. 11 is a block diagram of an example control system that may be usedwith an existing tool whereby an operator can fashion a workpieceincorporating the concepts described herein

DETAILED DESCRIPTION

It should be noted that the drawings are not true to scale. Further,various parts of the elements have not been drawn to scale. Certaindimensions have been exaggerated in relation to other dimensions inorder to provide a clearer illustration and understanding of the presentdescribed examples.

In addition, although the examples illustrated herein are shown intwo-dimensional views with various regions having height and width, itshould be clearly understood that these regions are illustrations ofonly a portion of a device that is actually a three-dimensionalstructure. Accordingly, these regions will have three dimensions,including height, width, and depth, when incorporated in an actualdevice.

A new power tool concept described herein has been created that allows ahuman or machine operator to control and operate the power tools withgreater finesse to provide a more manageable and accurately controlledrate of work on the workpiece that can be comparable to the use ofmanual tools, yet executed with the efficiency and productivity ofmodern power tools. The term “rate of work” herein refers to eithermaterial removal rate, or the rate of material surface alteration suchas in buffing, or other surface finishing due to heat and pressure, orcombinations thereof. The rate of work is related to the functional oroperating speed at a working surface on the power tool and the level ofpressure applied by the operator, or proxy, to the tool. “Functionalspeed” or “operating speed” as used herein refers to the rotational orlinear mechanical displacement rate (the rate of change of its position)or combinations thereof of the working surface with respect to time.Units of functional or operating speed may include revolutions perminute (RPM) as a measure of the frequency of a rotation or rotationalspeed such as with drills, rotary sanders, etc. RPM represents thenumber of turns completed in one minute around a fixed axis. Units offunctional or operating speed may also include oscillations per minute(OPM) for reciprocating working surfaces such as with jigsaws, vibratingsanders, etc. Simple linear speed units (velocity such as feet perminute) may be used for functional or operating speed in such tools asband saws, belt sanders, etc.

These new power tools allow an operator to more finely determine adesired rate of work and operating speed of the power tools by adjustingthe amount of force exerted between a workpiece and a working surface.In fact, at low workpiece forces, these new tools allow for reducing therate of work by as much as one-half and generally more, compared totypical embodiments, while the rate of work at the maximum operatingspeed of the new tools is substantially the same as a fixed speedconventional tool. Such improved control by an operator of the new powertool also allows for fine manual adjustment of the placement of theworkpiece with respect to the power tool, especially at first workpiececontact with the tool. By allowing for increased operator control overrotary, linear, or reciprocating motion of a power-driven tool's workingsurface, the rate of work as a function of tool speed and force (alsoreferred to as pressure or load) between the tool and the workpiece isfar more accurately controlled by an operator than with existing powertools, allowing for more efficient and accurate fine-crafting ofworkpieces. Also, energy may be conserved by allowing the new powertools to return to an initial speed once workpiece force is reduced orremoved.

For instance, with existing power tools, when a workpiece first contactsa quickly moving working surface, the workpiece is often gouged, jerked,or otherwise misengages with the working surface of the tool. Thisproblem is solved or greatly reduced with tools made incorporating thetechnique of the power tool 10 examples. This new technique allows foran improved motion actuator operating speed control that, as opposed tocurrently available modes of motor speed control, is workpieceload-responsive throughout its entire operating range. The techniquedescribed herein is applicable to all types of power tool tasks withvarious types of working surfaces that modify or remove workpiecematerial, such as sanding, grinding, drilling, honing, buffing,polishing, and saw-cutting just to name a few. Accordingly, a workingsurface includes, but is not limited to, a finishing surface, a cuttingsurface, a machining surface, a polishing surface, a buffing surface, orother material modifying surface. The working surface may be a singleitem such as a drill bit, or it may be an assembly of multiple partssuch as with a sanding assembly, which may also include additionalinertia. The power tool can include specialty medical powered tools toincrease the productivity and skill of a dentist, dermatologist, orother operator. Additionally, the work-piece may include biologicalsurfaces such as teeth and skin, and the working surface may be a toothdrill, a tooth polisher, a skin buffer, or dermal removal pad as a fewexamples.

The workpiece force aspect of the speed control can be determined fromdetection of a force or moment of force (such as torque or a leveredforce) that is imposed on the tool by an operator through the workpiecewith a force detector. One advantage to this new technique is improvedmanual control of a power tool applied to a stationary workpiece by theoperator. Another advantage is improved manual control over the handlingof a workpiece manually fed by the operator to a stationary power toolhaving a motion actuated working surface. Such improved control allowsfor the reduction or elimination of secondary sanding, honing, filing,or other operations to create finely crafted precision workpieces thatare now typically finished by hand with less efficient finishing tools,or with multiple machine operations. Yet another advantage is increasedsafety in the operation of a power tool.

As an example in an existing tool, such as a fixed-speed sander, asanding disc typically rotates with such high speed that an operator hasto gingerly or lightly hold the workpiece to the sanding wheel so as toavoid accidentally gouging, marring, over-cutting, or mis-shaping theworkpiece because of uncontrolled contact pressure and alignment. Thisposes two problems. First, without sufficient workpiece engagementforce, manual control is diminished because the operator must rely onhis/her fine motor skills so as to readily maintain the position andalignment of the workpiece while engaging it against the rotating wheelwithout unintentional removal of material. Second, once engaged,maintaining the alignment or constant change of the angle of theworkpiece against the sanding wheel is difficult for the same reason,for example as in finely shaping a curved portion of the workpiece. Theworkpiece can also fly out of an operator's hand when increased pressureis applied to the rapidly moving fixed-speed sanding wheel. Selectablefixed-speed power tools can be operated at lower speeds to providegreater operator control, but at a severely lower efficiency. Operatorcontrolled variable speed tools exist, but require the use of theoperator's hand, foot, or knee to control speed and thus increase theskill, dexterity, and training needed to perform fine work.

In some examples with the concepts described herein, the workpiece forceresponse can be tailored for delicate power tool operations such asfinessing a workpiece by hand with a power sanding disc that requires arate of work that is more controllable than is possible with existingpower tools. In one example, an operator can press the workpiece to thesanding disc working surface to increase the speed or decrease the speedof the sanding disc in proportion to the pressure used, therebymanageably controlling the rate of abrasion according to the immediatedemand for the rate of work. This ability of the operator to be incharge of controlling operating speed is done using a predeterminedcontinuous response profile (or “sensitivity profile” or “sensitivityprofile response” used herein for brevity), which may be single-valuedor within a range of values. This sensitivity profile describes arelationship between the amount of pressure, load, force, or moment offorce detected on the working surface and the tool's response, such asoperating speed of the working surface or tool output power. Thesensitivity profile, or sensitivity profile response, while arelationship of derived force between the workpiece and the workingsurface and observed work rate by an operator, may be implemented as a‘derived force’ vs. ‘motion actuator’ power function where power to themotion actuator is calibrated or otherwise characterized to achieve anestimated operating speed of a working surface for engaging theworkpiece.

Multiple or ‘two or more’ sensitivity profile responses may be availablefor the operator to select from with the new power tool. For example,the operator may select a relatively flat slow speed transition regionwhich changes over to a gradually increasing region that further tapersto a gradually flattening region at the maximum speed of the motor. Thevarious sensitivity profile settings which select a desired sensitivityprofile begin from a minimum or initial speed and extend to a finalspeed. The initial speed setting can be fixed or pre-set by the operatorand can include zero speed. A maximum speed setting can also be fixed,pre-set by the operator, or governed by the maximum torque of a motionactuator.

More generally, a power tool for operating on a workpiece is handled bya human or machine operator. A motion actuator of the tool ismechanically coupled to a working surface that is configured to engagethe workpiece. A controller is coupled to the motion actuator to controleither speed of the working surface or the amount of power delivered bythe motion actuator to the working surface. A force detector is coupledto the controller and configured to represent a derived amount of force,which represents the force or moment of force applied between theworkpiece on the working surface by the operator. The controller,configured with a predetermined continuous response profile (sensitivityprofile or sensitivity profile response), allows the operator tomanageably control with finesse simultaneously both a rate of work onthe workpiece and a speed of the motion actuator with the amount offorce, or moment of force, applied between the workpiece and the workingsurface. The controller may control an operating speed of the motionactuator based on a sensitivity profile with respect to the amount offorce the workpiece exerts at the working surface, and increase theamount of force required to achieve a particular rate of work on theworkpiece (compared to a fixed speed tool operating at the max speed).Accordingly, the controller allows for a lower rate of work (compared toa fixed speed tool operating at the max speed) for substantially allderived amounts of force greater than zero and less than a max derivedamount of force at a max speed for the new power tool.

The force detector determines and outputs a signal that represents theamount of force, or moment of force, or pressure applied between theworkpiece and working surface. This force may be either direct orindirect, such as by applying pressure to a tool which engages theworkpiece and transfers at least a portion of that applied pressure ontothe workpiece. There are several techniques to detect the force appliedto the workpiece and derive an estimation or representation of suchdetected force to create a “derived force.” One approach is to sense achange in the motion actuator load (such as moment of force), whichrepresents the “workload force” on the workpiece, which is a function ofthe actual force exerted by the operator. Another way is to sense arelated electrical motor parameter such as current, phase lag, orfrequency lag, or other parameter, depending on motor type. Another wayis to sense the actual force of the workpiece on the tool's workingsurface. For instance, one could have a strain gauge in the tool thatmeasures either the axial force (normal to a rotating or a reciprocatingplane of a working surface) or the radial force on the motion actuator.Also, one could have a force sensor embedded in the workpiece (orattached to it) and relay the amount of actual force to the controller.A “derived force on the workpiece” is an input (see x-axis on FIGS. 3,5A & 5B) to a controller implementing a speed or power sensitivityprofile and having an expected operating speed of the tool (which anoperator may observe) as the output (see y-axis on FIGS. 3, 5A & 5B) ofthe sensitivity profile.

The “derived force” is a representation of that force that is sensed orotherwise determined to be exerted by the workpiece, directly orindirectly, on the tool. Depending on how it is measured, it mayrepresent either workpiece force on the working surface, or moment offorce on the tool due to workpiece force, or a combination of theseforces. For some tools, the moment of force on the tool (while alsodependent on other factors) is a function of the axial force; in thesecases, a zero axial force by the operator results in a zero moment offorce on the tool. The force detector can be calibrated as needed toremove any non-linearities in the tool or tool's sensor(s), or keep themif desirable, depending on the design of the predetermined continuousresponse sensitivity profile. Further, there are multiple vectors ormoments of force that may be detected but the “derived force” will be atleast a partial function of the actual force exerted by the operator,which is being used to control a speed or power level close to thatindicated by a selected sensitivity profile. In some cases, an operatormay apply an axial or radial force, which results in a moment on thetool, which may be measured by various means such as motor current orframe flex. The force detector might use one or more sensor signals orother techniques to estimate the operator applied force to the workpieceand algorithmically manipulate to a standard signal so the samecontroller may be used with multiple tools independent on how the“derived force” is actually sensed for a particular tool. Thus, theforce detector output may be standardized, representing a predeterminedforce output function independent of how the amount of force theoperator applies on the workpiece is derived. A minimum “derived force”may be zero or some non-zero value based on particular toolimplementations.

If the sensitivity profile 50 is monotonically increasing, thecontroller is configured to increase, or not decrease, the power to theworking surface (generally thereby increasing speed, aka acceleration,or not decreasing speed) when the force detector represents an increasein derived force; it also decreases the power to the working surface(generally thereby decreasing speed, aka deceleration, or not increasingspeed) and/or applies braking to the motor actuator 14 when the forcedetector represents a decrease in force. If the sensitivity profile 50is monotonically decreasing, the controller is configured to increase,decrease, or maintain the power to the working surface and/or applybraking to the motor actuator 14 when the force detector represents anincrease in derived force, thereby generally decreasing speed, akadeceleration), and the controller is configured to increase, decrease,or maintain the power to the working surface (generally increasingspeed, aka acceleration) when the force detector represents a decreasein derived force. The controller may allow for selection of an initialspeed and/or a max speed. The predetermined continuous response orsensitivity profile to the amount of force applied by the operator tothe workpiece on the working surface may be configured to only respondin a range between an initial speed and a max speed. The tool mayinclude a sensitivity selector configured to apply one of ‘two or more’sensitivity profiles that represent a particular predeterminedcontinuous response profile selected by the operator, or the tool mighthave a continuously variable potentiometer or switched values as a userinput to vary the sensitivity profile.

The actual speed observed by the operator may not be exactly thatreflected in the sensitivity profile. For instance, there may be somehysteresis within the controller for making a decision of when to changethe power to the motion actuator to eliminate noise, sampling issues,component variances, and time delays due to processing, inertia, etc.Other errors may occur due to part variances and frictional losses.Also, the controller, in the process of implementing the sensitivityprofile, typically needs time to measure and react, also, the workingsurface and the assembly that attaches to the working surface hasnon-zero inertia that slows convergence to new speed values; therefore,there are likely to be temporal offsets from the desired sensitivityprofile. Further, one advantage of the power tool 10 examples is thatthe actual speed observed by the operator need not be perfectly matchedto the predetermined continuous response profile as the operator willmanageably adjust workpiece pressure as necessary to get a desired speedand rate of work. Accordingly, the controller may be configured to adaptthe speed of the motion actuator within a sufficient time period tosubstantially allow the operator to manageably control with finesseunder both acceleration and deceleration the rate of work on theworkpiece based on an applied force the operator exerts on the workpieceto the working surface.

Accordingly, the concepts described herein enable a power tool that canextend an artisan's natural crafting abilities to machine fashionedarticles, expanding the amount, type, and conception of artisticcreations possible while also reducing the effort, time, and focusneeded to create works of art or accurately made utilitarian articles.In fact, the one or more predetermined continuous responses orsensitivity profiles allow any electrical, mechanical, or othertolerances of the motion actuator, controller, and force detector to becompensated for by the finessed control of the artisan operator. Byallowing the operator to contribute to the feedback within the motionactuator control system, not only is the ability and productivity of theartisan operator increased, but unwanted tolerances, wear factors, orother machine inaccuracies can be compensated by the operator's finessedinput, thereby lowering ongoing maintenance of the tool. An added bonusis that energy is also conserved due to average lower operating speedsthereby further reducing operating costs.

FIG. 1 is an example block diagram of a tool 10 with a working surface16 that implements the concepts described herein. The working surfacemay be an abrasive surface, a drill bit, a saw blade, a knife blade, apolishing surface or other material finishing surface. The tool 10actuates a working surface 16 which operates on a workpiece 28, eitherby having an operator 12 apply an operator force 30 on the workpiece 28which transfers force to the working surface 16 or by having theoperator 12 apply an operator-tool force 21 on the tool 10 and the toolindirectly applying that force on the workpiece 28 via indirect toolforces 23A to the working surface 16 and 23B from the working surface 16to the workpiece 28. The tool 10 may include the working surface 16,which is configured to engage the workpiece 28 but the tool 10 may bealternately configured to couple to working surface 16 so it can beinterchanged as necessary. A motion actuator 14 is coupled 37 to theworking surface 16. The motion actuator 14 can be a rotary motor, suchas a brushless DC, brushed DC, single or multiphase AC, a pneumaticmotor, or hydraulic motor, just to name a few. Also, motion actuator 14could be a linear actuator such as an electrical solenoid, areciprocating motor, a pneumatic linear actuator or a hydraulic linearactuator, just to name a few.

A controller such as controller 20 is coupled 36 to the motion actuator14 to control the amount of power or speed delivered by the motionactuator 14 to the working surface 16. A force detector 18 is coupled tothe controller 20 and is configured to receive a force value 34 thatrepresents the force, load, or pressure on the working surface 16, whichan operator 12 applies from the workpiece 28 onto the working surface 16and outputs a signal that represents a derived force 35. The controller20 may include an inherent or explicit sensitivity profile 50 expressinga relationship between the derived amount of force and the operatingspeed of the working surface, under both acceleration and deceleration.The controller 20 may also have a sensitivity controller 19 implementingthe sensitivity profile 50 to allow the operator 12 to control withfinesse simultaneously both a rate of work from the workpiece and aspeed of the motion actuator 14 based on a predetermined continuousresponse in sensitivity profile 50 (see FIG. 3 and FIGS. 5A & 5B) to theamount of force applied by the operator 12 on the workpiece 28 at theworking surface 16.

The controller 20 may be configured to increase the speed of, or powerto, the working surface 16 via motion actuator 14 when the controller 20and force detector 18 determine an increase in force above a firstpredetermined amount and to decrease the power to the working surface 16when the controller 20 and force detector 18 determines a decrease inforce above a second predetermined amount.

The force detector 18 may be a standardized force detector representinga predetermined force-output function independent of how the amount ofdirect force 30 (or indirect forces 21 and 23A and 23B) the operator 12applies on the workpiece 28 is derived. For instance, there are severalmethods of detecting the amount of direct force 30 (or indirect forces21 and 23A and 23B) applied to the workpiece. For instance, there may bea rotational torque sensor on the motion actuator 14. Alternatively astrain gauge could be used to sense the linear or rotational forceapplied to the working surface. A strain sensor within the workpiece orattached to the workpiece can transmit a wired or wireless signal to theforce detector 18. If a pneumatic or other fluid based system is usedsuch as with hydraulics, the pneumatic or hydraulic pressures can besensed and sent to the force detector. In addition, if an electricalmotion actuator is used, a voltage sensor, current sensor, power sensor,frequency sensor, phase sensor, or other electrical property sensorcould be used. Accordingly, as there are many different possible ways tosense or otherwise derive the force the operator applies to theworkpiece, the force detector may convert a received signal into astandard format so that the controller 20 programming does notnecessarily need to be updated for different types of toolimplementations.

If the motion actuator 14, working surface 16, or rotating attachmentsto the working surface 16, on tool 10 have a high inertial momentum, thetool's motion actuator 14 may include a brake (17, 19 in FIG. 4). Thecontroller 20 may be configured to at least partially apply the brake(17, 19) when the controller 20 determines the need to reduce speed. Inaddition, the controller 20 of tool 10 may be configured to alternatelyapply the brake (17, 19) and the amount of power to the motion actuator14 when a need for speed reduction is determined The brake or otherdeceleration mechanism allows the controller 10 to adjust the motionactuator 14 speed in sufficient time to allow the tool operator tomanageably change simultaneously both the rate of work on the workpieceand the operating speed of the working surface even when the movingcomponents of the tool have a high inertial momentum.

Other possibilities to configure controller 20 are possible. Thecontroller 20 may allow for selection of an initial speed as a minimumspeed using an initial speed selector 24 via an initial speed input 39and a max speed using a max speed selector 26 via a max speed input 32.The sensitivity profile 50 (see FIG. 3) applied to the amount of forceon the workpiece at the working surface may be configured to only varyin a range between a selected initial speed and a selected max speed.However, there may be multiple sensitivity profiles 50 (see FIGS. 5A,5B, & 5C) available for an operator to choose from depending on operatorpreference and the type of work to be performed on the workpiece. Thisselection can be done with a sensitivity selector 22 via a sensitivityinput 38. The sensitivity selector 22 may be configured to select andapply one of two or more sensitivity profiles (see examples in FIGS. 5A& 5B) that represent the desired predetermined continuous response 50.While the sensitivity profile 50 may represent the relationship betweenthe derived force on the work-piece 28 and observed speed or power (as aproxy) applied to the motion actuator 14, the controller 20 of tool 10may control the power to the motion actuator 14 in discrete steps overmultiple time periods that approximate the sensitivity profile 50 with adigital calculation, reference look-up, or table to set the operatingspeed of the working surface. The controller's 20 use of the sensitivityprofile 50 allows any tolerances and other variability of the motionactuator 14, controller 20, and force detector 18 to be compensated forby the finessed control of the operator 12 as he/she applies theirartisan or skilled abilities to the workpiece 28 or tool 10.

In an example where a power source to motion actuator 14 is pneumatic orhydraulic rather than electric or a hybrid of electric, pneumatic,hydraulic, or combinations thereof, the controller 20 may be apneumatic, hydraulic, or hybrid logic controller that is an analog of acorresponding electronic control. For instance, a hydraulic or pneumaticpressure transducer as force detector 18 in the system can sense torqueor axial force. This force detector 18 can then control variouspneumatic or hydraulic controllers such as a hydraulic or pneumaticamplifier, a proportional valve for direct control, and a flow regulatoror pressure regulator just to name a few example non-electroniccontrollers 20. In some of these controllers 20, the sensitivity profile50 may be inherent in the design of the system and express arelationship between the derived amount of force and the operating speedof the working surface, under both acceleration and deceleration. Inother controllers 20, a sensitivity controller 19 may explicitlyimplement the sensitivity profile 50 and allow for tuning or selectionof the sensitivity profile 50 for operator preference or workrequirements.

FIG. 2 is another example of a tool 10′ having a controller 20controlling a motor 14′ (motion actuator 14), which is coupled to aworking surface 16. In this example, the controller 20 has a motorcontroller 40 that accepts inputs from a max speed selector, max speedselect 26, and a minimum speed selector, initial speed select 24. Thecontroller 20 also includes a sensitivity controller 19 that accepts aninput from sensitivity select 22 to allow for more than one sensitivityprofile. The motor controller 40 is coupled to a motor drive 42 unitthat is used to deliver power to motor 14′. The controller also has abrake drive 44 unit that is also coupled to the motor 14′ in order tohelp slow down the motor. In some examples, brake drive 44 may not berequired. Either of both the motor drive 42 and the brake drive 44 mayinclude additional sensitivity profiles to help respond adequately tobraking and acceleration.

The motor 14′ is coupled to a force detector 18. The force detector 18determines what operator force 30 is applied to the workpiece 28 byoperator 12 by measuring motor current as a proxy force value 34′ formotor load thereby creating derived force 35. The force detector 18, orcontroller 20 using force detector 18, may also determine the rate ofchange of operator force 30 or an estimation thereof (first timederivative) and/or determine the rate of the rate of change of operatorapplied force or an estimation thereof (second time derivative). Boththe rate of change and rate of the rate of change of the operatorapplied force may be positive or negative. In some examples, this forcedetector 18 may have a standardized output for derived force 35 suchthat the input to force detector 18 may come from one or more differentsensors or other detection mechanisms yet provide a compatible standardoutput to the controller 20. The operator 12 can observe either thespeed 43 of the working surface 16 or the rate of work 31 (materialremoval in this example) from the workpiece 28 or both. To get thedesired rate of work, in some configurations the operator can adjust thelocation of the workpiece 28 on the working surface and/or the forceasserted on the workpiece to change of the speed of the tool 10.

The sensitivity select 22, max select 26 and the initial select 24 mayinclude switches, potentiometers or other devices to allow for multipleor variable selections. If needed or desired, an analog to digital (A/D)or digital to analog (D/A) conversion circuit can be implemented betweenthe max select 26, initial select 24, sensitivity select 22 and thecontroller 20. Other interfaces, to and from the controller 20, mayinclude signal filters, D/A, or A/D circuits.

FIG. 3 is an example chart detailing the observed speed of the workingsurface 16 by the operator 12 based on a derived force 35 applied to theworkpiece by the operator 12. The controller 20 may be configured tocontrol the motor 14′ within a control range 54, based on derived force35. The control range 54 is bounded between a zero (none) derived forceand a max derived force 59. The example of FIG. 3 shows a startingderived force of none or zero, corresponding to an initial speed 55, anda max derived force, corresponding to a max speed 56, the startingderived force may be larger than zero and the max derived force may beless than the tool's maximum possible derived force. The control regionis bounded between an initial speed 55 when there is no or a minimumderived force 35 detected and a max speed 56 when there is a maximumderived force 35 detected. In some examples of tool 10, these bounds maybe fixed limits In other examples one or both the max speed and initialspeeds may be set by an operator or other person or device. When thetool 10 is powered and the workpiece 28 is not in contact with theworking surface 16, the derived force is usually determined to be noneor zero (0) though there could be a non-zero minimum derived force thatrepresents motor inefficiencies at initial speed 55, other frictionaleffects, or noise floors. This results in the controller outputting apower to the motor 14′ (or other motion actuator 14) to operate the tool10 at the initial speed 55. As operator force 30 exerted by the operator12 on the workpiece 28 is sampled or otherwise derived, the speed of themotor 14′ is adjusted by changing the amount of power supplied to themotor 14′ by the controller 20 according to sensitivity profile 50,between the zero derived force and a maximum derived force 59, when themax speed 56 is reached. In this example, once the max speed 56 isreached, the controller 20 response is undefined 57 and can varydepending on various implementations and could maintain max speed, dropoff, or continue to increase to the max motor limit 58. In otherexamples, there may be no max speed 56 imposed and the controller willfollow a sensitivity profile 50 until a max derived force 59 at the maxmotor limit 58 is reached. In some examples, sensitivity profile 50 maybe a sensitivity profile range 51 due to variances of the motionactuator, the controller, the force detector, or by design. That is, animplemented sensitivity profile may not always have a single-valuedresponse due to the variances or purposely by design. For instance, insome examples, the sensitivity profile range may be designed to have arandom component to the sensitivity profile response in order to reduceelectromagnetic interference (EMI) or help in control system stability.

FIG. 4 is an exemplary drawing of a motion actuator 14 configured as amotor 14′with one or more braking mechanisms. One type of brakingmechanism may be a mechanical brake 17 which operates via frictionalforces to slow the motor shaft 11 which is coupled to the workingsurface 16 via a coupling 13. Alternatively, or in addition tomechanical brake 17, one or more electrical brakes 19 can be used toapply a counter electromotive force on the rotor 15. Mechanical brake 17may also be implemented using pneumatic and hydraulic components and mayalso be some hybrid of electrical, mechanical, pneumatic, or hydrauliccomponents. Depending on the tool type, if the working surface isattached to a body or assembly having a high momentum or inertia, thensimply reducing the power to the motor may not be sufficient to allowthe tool to respond properly to the operator's change of load on theworkpiece 28. By using braking along with intermittent power control inseparate or same time intervals, the controller 20 is able to quicklyand responsively match the speed of the motor to the sensitivity profile50 as in FIG. 3 by using the derived force on the workpiece. By havingthe controller 20 quickly match the speed of the motor based thesensitivity profile 50, the operator is able to manageably changesimultaneously both a rate of work on the workpiece and the operatingspeed of the working surface by applying a single force from theworkpiece onto the working surface 16 of tool 10.

FIG. 5A is an example graph of various possible sensitivity selectionprofiles 50 (such as 61, 62, 63, 64, 65, 66, 67, 68, and 69) thatprovide different tool operating characteristics. Other sensitivityselection profiles are possible beside these examples. In addition,there may also be additional sensitivity profiles or look-up tables usedto control braking and acceleration. In some tool examples, there may betwo or more sensitivity profiles 50 to allow the operator to choose thederived force 35 along a derived force range 33 and respective motionactuator speed pairing between an initial speed 24 and max speed 26,both of which may be adjustable. Accordingly, the control system 20 canfollow one of a plurality of predetermined and preset speed-force curvesthat are operator selectable. The sensitivity profiles 50 may be afamily of substantially monotonically increasing curves of positiveslope (but could also have some negative slope, a monotonicallydecreasing region, in some examples) and are predetermined single-valued(only one Y-axis value for each X-axis value) continuous responses,wherein the curve limits may be defined between an initial speed 24 anda max speed 26 which is greater than the initial speed 24. The max speed26 may in some examples correspond to the maximum allowable torque ofthe motor or other motion actuator 14. The max speed 26 and initialspeed 24 adjustments do not clip the sensitivity profile curves butrather just set the lower and upper speed bounds and the controller 20scales the sensitivity profiles accordingly within the initial and maxspeed bounds.

By way of one example, if a sensitivity profile 50 is selected wherebythe initial portion of the curve is relatively flat with load, such aslower tapered profile 64, a workpiece 28, such as the end of a woodendowel, may be initially pressed against a sanding machine rotating at aslow finite initial speed with adequate pressure for workpiece alignmentwith the working surface. This speed-pressure or speed-load relationshipallows the operator 12 to hold and align the workpiece 28 securely withrespect to the working surface 16 of the disc, without the workpiece 28jerking or skipping out of alignment (or from the operator's 12 grip) bycause of friction with a rapidly moving abrasive surface such as withconventional sanding or grinding machines. This lower tapered profile 64also helps prevent gouging or otherwise accidentally causing unwantedmaterial removal from the workpiece 28, as may be the case if thesanding disc were rotating rapidly upon initial contact with theworkpiece. Thus, the operator 12 can confidently grasp the workpiece 28while applying sufficient muscular force in the fingers and wrist tomaintain control, and press the workpiece 28 against the sanding wheelwith sufficient pressure so as to accurately make the initial alignmentbefore any significant material removal 31 from the workpiece 28 occurs.This lower tapered profile 64 allows for an expansion in the exertedforce range at low speeds to achieve a desired rate of work.Alternatively stated, the lower tapered profile 64 reduces the initialrate of work for a given exerted force on the workpiece than if thatsame force were exerted on a workpiece to a conventional fixed speedtool having a fixed speed at a speed above the initial engagement speedof the new power tool 10.

In a conventional tool example, an operator wielding a hand-heldelectric drill with a standard drill bit may contact the tip of thedrill to a stationary workpiece with a smooth surface without thebenefit of a pilot hole or center punch indentation. Normally, the drillbit working surface will wander from the initial point of contact whenthe drill motor is engaged. In this example, the drill has a zeroinitial speed; however, when the operator engages the drill bit on thesurface and presses the trigger motor speed control, the speed of themotor increases rapidly to a fixed maximum speed, making the bit jerk orwander laterally as its tip is pulled along the surface, instead ofembedding into the surface to start the hole. To control this somewhat,if the drill has a variable speed trigger control, the operator canpartially press the trigger speed control to slow the rotation of thebit in order to prevent the bit from wandering. However, the operatormust simultaneously apply pressure on the drill bit, which can stop themotor because the torque is low at low speeds.

The present power tool 10 examples allow the rotational speed of a drillto respond to the load on the motor by the pressure applied to the drillbit, rather than requiring drill trigger motor speed control by theoperator. In this example using the power tool 10 examples, asensitivity profile 50 is chosen to have a first slope of low value andat least a second slope of substantially higher value than the firstsuch as with lowered taper profile 64 or extended lowered taper profile63. This profile 63 increases the speed very slowly in response toincrease derived force and then rapidly increases speed over a narrowrange of derived force. Upon initial engagement, the operator firstaccurately centers the drill bit at zero initial speed, and then beginsto increase pressure on the drill which transfers the force to theworkpiece and the controller 20 gradually increases the rotational speedover an initial range of derived force. The gradual increase in drillspeed with increasing load allows the bit to form a shallow indentationpreventing the bit from wandering at higher speeds, yet the controller20 maintains a high enough power level to overcome friction when the bitis pressed into the workpiece at slow speeds. As the operator 12 furtherincreases the amount of force applied to the workpiece 28, the drillspeed rapidly increases to a maximum speed according to the selectedsensitivity profile 50. In this way, a hole can be drilled accurately onsurfaces such as where pre-made guidance holes are not possible.

In one example, arch profile 67 may be advantageous with polishing orbuffing tools. As shown, arch profile 67 has a curve that arcs up to amax speed with an applied derived force 35 less than the max possiblederived force 35. The arch profile 67 then arches down somewhat athigher derived forces 35. When buffing out a workpiece and operating ator near the max derived force 35, the workpiece may tend to overheat.However, one might need continued high pressure to enable efficientaction of the polishing media. With arch profile 67, one can polish at ahigh pressure and moderate speed, then back off on pressure, therebyhaving a lower derived force 35, and have the advantage of higher speedand low pressure to remove the polishing compound or give a betterluster as a result of high speed and low friction. Accordingly, archprofile 67 may have a first region (1^(st) region) where the operatingspeed is managed by the operator to control simultaneously the rate ofwork on the workpiece and the operating speed of the working surface,and a second region (2^(nd) region) where the operator is able to alsosimultaneously control the rate of work on the workpiece and theoperating speed of the working surface but wherein the operating speedis reduced as the operator applied force is increased in order toperform work at low speed and high friction, lower material removalrate, or limit workpiece temperature. The first region of arch profile67 is monotonically increasing and the second region is monotonicallydecreasing. Accordingly, a sensitivity profile 50 may have at least oneregion with a monotonically decreasing region and possibly moredepending on the desired response between the derived force 35 and theobserved speed output. The high point of the arch may be set by theoperator in some examples, in other examples, the high point may be setat manufacture, or by the tool based on temperature readings fromadditional sensors (not shown) coupled to the controller 20.

In another example, first s-shaped profile 68 may be advantageous with areciprocating motion actuator 14, such as a hand-held jigsaw. In thecase of the jig-saw, the blade motion is reciprocating, therefore, thefrequency of the reciprocating motion is observed by the operator as itsspeed. When an operator 12 positions a blade of a jig-saw on a workpieceit can wander or jump at the beginning of a cut when the saw motor isengaged. However, with the power tool 10 examples, a hand-held jig-sawusing a profile such as s-shaped profile 68 has a 1st segment (1^(st)seg) of slowly increasing speed with force followed by a 2nd segment(2^(nd) seg) of a faster increasing speed with force, and then followedwith a 3^(rd) (3^(rd) seg) segment of segment of slower increasing speedwith force. This profile allows an operator 12 to accurately engage thejig-saw blade and apply whatever force is necessary to engage the bladewith the workpiece and then apply additional force without causing thereciprocating blade to significantly increase its speed the until 2^(nd)segment is reached but maintain a desired rate of work depending on thethickness or hardness of the workpiece. If the operator encounters aregion in the workpiece material where more precision is needed alongwith productivity, the operator 12 can increase the amount of forceapplied and enter the 3^(rd) segment which allows for more operatorcontrol than the 2^(nd) segment during periods of fast material removal.

The material removal rate is alternatively referred to in some scenariosas the workpiece feed rate as understood by those skilled in the art.Within usability bounds, the material removal rate increases withincreasing motor speed and force applied to the workpiece 28 against thework interface of the power tool such as working surface 16. For theasymmetric s-shaped profile 68 example, the choice of speed-load slopetransition values can determine how much operator force 30 to apply tothe workpiece 28 to obtain a degree of fine control over the materialremoval rate and therefore the shaping of the workpiece 28. The degreeof fine control is related to the experience and skill of the operator12. In particular, the operator 12 relies on manual dexterity andexperience to apply optimal force on the workpiece 28 to effect amaterial removal rate that is not too great and not too small. Thismaterial removal rate is a function of motor speed, for example therotational speed of a disk sander, and workpiece pressure, and now theoperator 12 can control the motor speed via the amount of operator force30 applied to the workpiece 28. Advantageously, an operator's control inshaping a workpiece 28 is enhanced when the operator 12 can command themotor 14′ to provide speeds that allow him or her to achieve optimalmanipulation or finesse of a workpiece 28. The power tool 10 exampleFIG. 2 provides one or more sensitivity profiles 50 tailored to thecontroller 20 to automatically adjust the power or tool motor speed inorder to allow optimal performance of the power tool 10 for variousdifferent work requirements.

In some examples, especially with digital or discrete controllers, thesensitivity profile 50 may have a stepped profile that approximates oneof the continuous profiles in discrete or quantified values to allow forvarious ranges where speed is constant for a range of forces such aswith stepped profile 65. The sensitivity profile 50 may also have astepped profile due to digitization artifacts if implemented in adigital controller.

In another example, a second s-shaped profile 69 would allow for greaterrange of speed adjustment at low ranges of force in a first segment(1^(st) seg′), followed by a second segment (2^(nd) seg′) with a lesserchange in speed due to a change in force. This would allow an operator12 to engage the work-piece at low speed and with additional forcequickly settle into a higher speed range with a nearly constant orslightly increasing speed over a wide range of force. If substantiallygreater material removal is desired, the operator 12 can increase theforce and operate in a third segment (3^(rd) seg′) that has a rapidlyincreasing speed to force ratio, allowing the operator 12 continuedspeed control but also greater productivity. In some examples, thespeed-force profile can be straight throughout the entire derived forcerange such as with straight profile 62 or its digital approximation 65.In other examples, perhaps just the upper portion of the profile istapered, such as in upper tapered profile 66, to allow the operator morecontrol as he/she is approaching the load limit of the tool.

In addition to just having a set of sensitivity profiles 50 loaded intothe tool 10 for selection by operator 12, other examples of tool 10allow an operator 12 to adjust and thus predetermine the shape of thecontinuous response desired for a particular job. In this example, theoperator 12 has the ability to manipulate the shape of the sensitivitycurve at will. The operator 12 is presented a general speed-load orspeed-force sensitivity profile curve on a display such as an LCDdisplay. Using a cursor to move the slope transition points, theoperator can freely select the slope transaction load values, expandingor compressing the rapidly increasing portion of the sensitivityprofile. Moreover, the operator may also select the maximum and minimummotor speeds, changing the vertical extent of the speed-load orspeed-force sensitivity profile. In this manner, the power tool 10examples advantageously provides a technique to readily and easilyadjust the speed of the power tool motion actuator 14 to suit thespecific workpiece shaping operation.

Yet still in other examples, sensitivity selection profiles 60′ havingdiverse shapes are also possible using polynomial equations and changingone or more variables as shown in FIG. 5B. In this manner, a digitalmicroprocessor may calculate the sensitivity without relying on theexpense or unavailability of memory elements to store thousands of lookup values. A plurality of numerical curves that represent motor controlsensitivity profiles 50 based on Y=X^(a)+initial speed are plotted inFIG. 5B. These numerical curves are labeled X¹, X², etc. to denote theraised polynomial used but actual formulas can include scalar and offsetvalues such as Y=c*X^(a)+b, where “a” is the raised polynomial value,“b” is an offset value, and “c” is a scalar value. In this example,these profiles 161-169 are a family of simple raised polynomial curvesof the type Y=X^(a)+initial speed where exponent “a” can be any positiverational number typically within 0.01 to 100, and more specifically 0.25to 8. A conventional constant speed tool has the form Y=c*X⁰ (note thatX⁰=1) where “c” is the speed adjustment. In this example, X representsthe derived force 35 axis having derived force range 33 from none (0) tosome determined max derived force based on design parameters such as themaximum load of the motion actuator 14 and signal transformationrequirements of the controller. The value Y represents the observedoperational speed of the working surface 16 by operator 12. The familyof curves define a space bounded by two simple polynomial curves, onehaving an exponent a=0.01 and the second having a=100, wherein “a” takeson all possible values between 0.01 and 100 generating a family ofcurves of infinite number fitting within the bounded space. Moreover,the bounded space defined by Y=X^(0.01) and Y=X¹⁰⁰, where X=0 toX_(max)=maximum derived force and Y=0 to Y_(max)=maximum observed speed,may include any curve of arbitrary curvature with the bounded space(such as in FIG. 5A), and not just simple polynomial curves. As anexample, in FIG. 5A, first and second s-shaped profiles 68, 69 shownwould be contained within the space delimited by Y=X^(0.01) and Y=X¹⁰⁰whereas the proifile Y=c*X⁰ of a conventional constant speed tool wouldnot be wholly contained.

Accordingly, in some examples, the number of sensitivity profiles thatare made available to an operator 12 to choose may be limited to afinite number of two or more profiles. These sensitivity profiles may berepresented in digital form by way of a data structure held with aphysical (tangible) non-transitory memory element, wherein the dataelement includes a multi-dimensional array containing a plurality ofone-dimensional sub-arrays, each sub-array containing a series ofmicro-processor readable data elements, wherein each of the dataelements represents a binary or other encoded value that is conveyed bya microprocessor unit to a digital-to-analog converter unit to be outputto the controller 20 as an analog voltage or power signal. The ensembleof binary data elements in each sub-array represents a pre-calculatedsensitivity profile for selected use as sensitivity profile 50.Alternatively, the sensitivity profiles may be represented by equationsor algorithms in computer readable code, or analog electronic,pneumatic, hydraulic, or other mechanical means and executed duringoperation.

FIGS. 6A and 6B are flowcharts 70 and 70′ for an “Alberti Algorithm” oftwo example methods for implementing the power tool 10 examples withcontroller 20 for sensitivity profiles 50. Controller 20 may be coupledto one or more sensors or other detection techniques to help derive theamount of force exerted on workpiece 28 by operator 12 to emulate orvirtualize force detector 18. For instance, force detector 18 canreceive input from sensors capable of sensing mechanical loads, such asmotor torque and axial or radial load on the tool. In other examples,force detector 18 may receive electrical signals that allow for thedetection of motor current, motor RPM (speed), hydraulic pressure, airpressure, acoustic waveforms, or optical signals. The controller 20 mayinclude a microprocessor, a digital signal processor, analog processing,ladder controller, an algorithmic control unit, hard-coded logic, afield programmable array, state machine, or combinations thereof. In oneexample, the controller 20 has a clock circuit which generates a signalat a fixed time interval or alternatively an event driven signal basedupon detected changes in sensor input. When a clock signal is used, thesensors can be sampled at some chosen time interval t, for example every1/10 seconds or 100 ms although any value from 1 ns to multiple secondsis possible, particularly 1/100 seconds or 10 ms, or the sensors may besampled multiple times per interval t and then averaged, or processed,with current, or past value sets, to arrive at the value that will beused.

At each time interval t, the controller 20 may begin a routine at startblock 71 to adjust the speed of the motion actuator 14 and workingsurface 16. First, the Force Detector 18 determines the amount of forceexerted on the workpiece 28 in derive force block 72 to create a derivedforce 35. The controller 20 may have tangible non-transitory computerreadable memory in which it can store previous, current, and futurederived forces to be able to determine the rate of change of the derivedforce, the rate at which that rate of change is occurring, and may alsoapply filtering to remove unwanted noise or other errors which mayarise. When a derived force is determined in derive force block 72, itcan be compared with one or more previous readings (delta—Δ) todetermine if the derived force is increasing in decision block 73 by afirst predetermined threshold. If the derived force is increasing overthe first predetermined threshold, then the controller 20 may in block76 adjust to increase or decrease the speed in FIG. 6A or, alternativelyin block 76′ in FIG. 6B, adjust to increase or decrease the power to themotion actuator 14 based on the currently selected sensitivity profile50 (increase or decrease based on respective increasing or decreasingsensitivity profile 50 region) or a function that enacts sensitivityprofile 50. In either example, corrections for inefficiency or inertiacan also be made. The corrections for inefficiency or inertia may bepositive or negative or a combination thereof depending on thecharacteristics of the particular system. The sensitivity profile 50 mayalso be stored in computer readable memory accessible by controller 20or it may be generated by analog circuitry and read by controller 20 viaan A/D convertor circuit or, by use of a comparator, compared against acalculated value. Once the power to the motor actuator 14 has beenincreased the flow goes back to the start block 71 to await the next tcycle.

If the derived force is determined to not be increasing by the firstpredetermined threshold in decision block 73, then a determination ismade using one or more previous readings whether the derived force isdecreasing by a second predetermined threshold in decision block 74. Ifthe derived force is decreasing by at least the second predeterminedthreshold, the controller may adjust to decrease or increase the speedin block 77 in FIG. 6A, or adjust to decrease or increase the power inblock 77′ in FIG. 6B, to the motion actuator 14 based on the currentlyselected sensitivity profile 50 (decrease, increase, or maintain basedon respective decreasing, increasing, or flat sensitivity profile 50region). Once again, in either example, corrections for inefficiency orinertia can be made. The first predetermined threshold may be the sameor different than the second predetermined threshold and both act as aform of hysteresis to help stabilize the tool.

Depending on the implementation, there may be more inertial momentumwith the motion actuator 14 and the working surface than can beadequately compensated for by just decreasing the power. In such asituation, the controller 20 may also provide braking as necessary,either mechanical or electrical. In some examples, it may be required toalternately reduce power and brake independently, particularly if themotion actuator uses common electrical motor coils for both drive andbraking and especially if the derive force signal also depends on theelectrical motor coil. The alternating power reduction and braking canbe done in a single time interval t or it can be alternatively done indifferent time intervals t depending on the chosen t interval period andthe design criteria for how much lag time can occur between a detectedforce transition and return to steady state of the motion actuator.After the power reduction or braking functions have completed in block77 in FIG. 6A or block 77′ in FIG. 6B, the flow goes back to the startblock 71 to await the next t cycle.

If the force is determined in block 75 to not be increasing by the firstpredetermined threshold or decreasing by the second predeterminedthreshold or the rate of change is only within a predeterminedhysteresis threshold (to prevent rapid changes due to noise or otherfluctuations), then in block 78 of FIG. 6A, the speed of, or in block78′ of FIG. 6B the power to the motion actuator is set and maintainedbased on the currently selected sensitivity profile 50 and flow returnsto block 71 to await the next t cycle. If for some reason, the systemdetermines that the current is not increasing, not decreasing or is notsubstantially constant and no action should be currently taken, thenflow returns to block 71 to await the next t cycle. This set ofthresholds allows for states of hysteresis within the control system toincrease stability and allow for slight variations in operator appliedforce without making unneeded changes unless the change of derived force35 meets designed thresholds.

In an example of power control, one can measure a motor's torque as oneapproach to arriving at a derived force 35 and use a power controlalgorithm to change the speed (RPM) of the motor. In order to simplifythe illustration of power control, it is assumed in the followingexamples that the system has very high efficiency and very lowrotational inertia. Various compensations, such as a higher power outputrequired due to inefficiencies (such as friction, motor inefficiencies,etc.), or temporal energy corrections to compensate inertia (such asadding extra drive power for RPM increase or added braking for RPMdecrease) may be done with additional algorithms and are notspecifically considered for these examples but would be known to thosepersons of skill in the art.

The following power algorithms and any aforementioned compensations maybe implemented by processors following instructions read from tangiblenon-transitory computer readable memory. Alternatively, the poweralgorithms and compensations can be pre-calculated or characterized forparticular systems and stored as look-up tables, databases, or listswithin the tangible non-transitory computer readable memory. In yetother example systems, the power algorithms may be implemented in analogform or be designed in as part of the inherent system architecture,including pneumatic, hydraulic, or mechanical controls that approximatedesired control curves.

Definitions:

-   -   T=measured torque    -   Tmax=maximum Torque    -   R=approximate (unmeasured) RPM    -   Rmax=maximum (unmeasured) RPM    -   P=output Power    -   InitialSpeed=RPM at zero workpiece torque (a constant that may        be set, programmed, or hardwired)    -   M=a positive scaling factor either by design or by user choice

Example 1

Example of power control to enact a straight line from point of zerotorque and InitialSpeed to a point of maximum torque and maximum speedwith a desired slope M=(Rmax−InitialSpeed)/Tmax:

Power Control to the motion actuator will approximate the speedrelationship: R=M*T+InitialSpeed

-   -   General power equation:

P=T*R

-   -   Desired RPM/Torque relationship:

R=M*T+InitialSpeed

The above equations can be combined to get a power control formula:

P=T*(M*T+InitialSpeed)

Note that this power control example implements a line similar to 164 inFIG. 5B with the consideration that torque is used to create the DerivedForce 35 and RPM is the Observed Speed and the power is the twomultiplied together. In terms of power, this form of control is alsosimilar to the X*X line 170 in FIG. 6C with consideration that torque isanalogous to X, or Derived Force 35.

Example 2

Example of power control to enact a scaled squared RPM relationship withtorque from point of zero torque and InitialSpeed and having desiredscaling factor M, M=(Rmax−InitialSpeed)/Tmax². Torque value may also bescaled by using the substitution of (K*T+J) for T in the final equation,where K and J are constants of choice:

General power equation:

P=T*R

-   -   Desired RPM/Torque relationship:

R=M*T ²+InitialSpeed

-   -   Combine equations to get power control formula:

P=T*(M*T ²+InitialSpeed)

Note that this power control example implements a line similar to 165 inFIG. 5B with the consideration that torque is used to create the DerivedForce 35 and RPM is the Observed Speed and the power is the twomultiplied together. In terms of power, this form of control is alsosimilar to the X*X² line 171 in FIG. 6C with consideration that torqueis analogous to X, or Derived Force 35.

FIG. 7 is an example flow chart 80 which the Force Detector 18, or aController 20 that incorporates a Force Detector 18, may use to readsensor or other sensory signals and convert to a standardized derivedforce signal. In block 81, a parameter from a sensor network of one ofmore sensors and indicators is read by Force Detector 18. In block 86,the parameter may be pre-filtered either with analog or digitalprocessing to remove noise, correct for abnormalities ornon-linearities, change scale, or remove undesired components orstatistical aberrations. In block 82, the read parameter, or filteredversion of it, is converted to an encoded digital signal which may bemanipulated by the Force Detector 18. The converted digital signal isthen filtered using analog or digital filtering or a combination thereofin block 83 to remove any unwanted noise, components, non-linearity, orstatistical aberrations. The filtered signal is then in block 84transformed mathematically into a standard format, such as by formula,look-up table, database, or other method. In block 85, the derived forceis then sent to the controller 20.

FIG. 8 is an example of controller 20 actions for a sequence of time ‘t’intervals 91 to illustrate when both power reduction and braking occurin a system where motor current is proportional to motor torque. Alsoshown in columns are Events 92, RPM 93 (motor speed, unmeasured andunknown to system, but included for understanding), Motor burden 94(unmeasured and unknown to system, but included for understanding),Measured Current 95, motor controller Mode and PWM (pulse-widthmodulated duty cycle) 96, Controller Notes 97, and RPM Notes 98. In thissimplified braking example a motion actuator 14 is a motor rated at 2000RPM (revolutions per minute) and 2 A (Amperes). In this simple example,the controller uses a sensitivity curve that is linear for currentsbetween 400 mA and 1100 mA, such that the characterized RPM atmanufacture had the same value as the current in mA (as will be shown,the controller RPM response will lag the desired RPM until a period ofno burden changes allows settling). The value of the Measured Current 95is utilized in this system as the Derived Force 35. No speed or RPMinformation is used in the algorithm of the controller 20 of thisexample and are shown for reference only, as an operator 12 may changethe force exerted on the workpiece 28 based on observed speed of themotor and therefore vary the motor speed based on the desired rate ofwork. For this example, motor current cannot be measured while braking,in some examples, motor current may be measured while braking. Also, theburden 94 on the motor is not directly measured and is shown forreference only to help explain the algorithm. The burden 94 in thisexample is a moment of force, or torque represented in N*cm(Newton-centimeters).

Initially at t=0 in this example, the operator 12 has workpiece 28pushed into the working surface 16 and is creating 100 N*cm(Newton-centimeters) of torque on the motor. The tool 10 is insteady-state at 1000 RPM and 1 A (1,000 mA). Then, over the next 0.5seconds, the operator 12 reduces the workpiece force 33 to 50 N*cm or ½of the previous torque load. In this example, the control loopimplemented by controller 20 is on 100 ms intervals but may be moretypically 10 ms intervals. However, to better illustrate the changesoccurring and keep the number of time intervals reasonable forexplanation, a longer period has been chosen. The physical system inthis example is illustrated to respond in sampled or discrete steps andassumes a very low inertia to help illustrate the changes occurring. Forthis example, some physical effects were simplified and math wasrounded. Motor burden 94 (the motor load) is not measured by thecontroller, but rather given as a condition stemming from operatorcontrol. Motor burden 94 is stated in N*cm, time (t) 91 is in 100 msintervals, measured current 95 to the motor is in mA ( 1/1000 A) and thepower applied to the motor is pulse width modulated (PWM) 96 in a dutycycle shown as a percentage of full (100%). Event 92 describes action ofthe workpiece 28 in relation to time (t) 91. Controller notes 97indicate results from actions taken by controller 20 due to operatorforce changes. Other notes 98 illustrate the expected RPM 93 of speedbased on controller actions.

At time t=0 the tool is in an initial steady-state, the RPM of the motoris 1000 and the load is 100 N*cm. The motor is drawing 1 A or 1000 mA asmeasured and the controller 20 is driving the motor at a 50% PWM dutycycle of full power. This 50% PWM duty cycle for the initialsteady-state drive PWM % is derived from a stored sensitivity profile50.

At time t=1, as noted by event 92, the operator 12 had reduced theworkpiece force against the tool resulting in a load of 90 N*cm on themotor. This reduced load caused the motor current to drop to 900 mA and,however, because there is a reduced load on the motor, its speed hasincreased to 1100 RPM which is in the opposite direction of what isdesired.

For instance, when the operator 12 initially reduces the workpiece forceagainst the tool, the motor has the same drive level but experiencesless load and may likely speed up and the controller 20 will need toreact to reduce the motor speed generally to stay on the sensitivityprofile 50. Various tool inefficiencies and drag, due to friction, airflow, etc., help to counteract the undesired motor speed-up, as does theactual workpiece load on the working surface, but they are not accountedfor in this simplified example. Additionally, for systems with highmoment of inertia, the speed-up will be attenuated. However, for largeworkpiece load decreases that demand large desired lower speed changesto the motor, braking may be needed. Tools with a higher moment ofinertia will require a larger change in rotational kinetic energy (RKE)that will especially benefit from braking, for example when fitted withheavy sanding disk fixturing. For such tools to decrease their RPM,there must be a corresponding loss of RKE. To enact high RPM lossrequires more energy dissipation due to more loss of RKE. Some factorswhere a high relative RKE amount may need to be quickly absorbed when anoperator decreases the derived workpiece force (which creates acorresponding load decrease on the motor) are:

-   -   1. Operator quickly lowers load;    -   2. A large tool moment of inertia;    -   3. A high tool speed;    -   4. A loss in workpiece derived force occurs across a steep slope        on the selected sensitivity profile;    -   5. A high system efficiency relative to the RKE loss (i.e. low        frictional factors for spinning, this is true for most systems,        however systems with low efficiency compared to the RKE loss        need less braking since the inefficiencies naturally slow the        speed and often need not be considered); and    -   6. Operator enacts a large decrease in load.

Because some sensitivity profiles require a reduction in tool speed (orRPM) for reductions in workpiece force, combinations of the variousfactors above may require energy dissipation that is well suited tobraking. However, small RKE decreases due to small motor load changes,or that occur at low speeds, or that occur slowly, or that occur whenthe selected sensitivity profile slope is “shallow” (i.e. nearzero-slope, not steep) may not need braking due to the other slowingfactors such as workpiece load, air friction or system inefficiencies.Thus, a braking command might require a minimal amount of derived load(current in this example) change before it occurs. The actual level ofbraking may depend on any, or, all of the above factors.

The RKE for an active portion of many tools (for example, all toolspinning parts that are connected to the working surface, such as asandpaper disk, a disk mount, a motor shaft, etc.) may be described by:

RKE=½*I*w ²

where:

RKE is the rotational kinetic energy

I is the moment of inertia relative to the stationary portion of thetool

w is the working surface rotational speed in radians per second

Since RPM is the rotations per minute of the motor and there are 2πradians per rotation and 60 seconds per minute, then:

w=(2*π)/60)*RPM=(π/30)*RPM

RKE=½*I*w ²=½*I*((π/30)*RPM)²=(I*π ²/1800)*RPM²

The amount of energy to transition to a lower RKE, say from an RKE1having RPM1 to an RKE2 having RPM2, where RKE1>RKE2, may be describedas:

ΔRKE=(I*π ²/1800)*(RPM1²−RPM2²)

This ΔRKE is the energy that must be dissipated for an RPM change andthis energy is therefore proportional to a difference in the squares ofthe two rotational speeds. Because this “Alberti Algorithm” does notrequire a controller to measure and react to tool speed (although itcould do so in some implementations), the ΔRKE for many systems cannotbe exactly known, however, approximations may be utilized based on theabove factors, which indicate when higher braking PWM may be needed, andmay be found at either run time (factors 1, 3, 4, 6), or the designphase of the product (factors 2, 5) and be accordingly compensated for.

At time t=2, the controller 20 compensates by applying a braking periodfor 10% of the time interval to slow the speed of the motor to 900 RPMor a reduction of 200 RPM. The braking percentage (PWM duty cycle) hadbeen previously customized for the system given the rate of speedchange, inertia, time and other considered factors from the list aboveto adequately converge on the sensitivity curve. Meanwhile, as theoperator 12 continues to lessen the applied force on the workpiece 28,the load on the motor drops to 80 N*cm. However, as braking is beingapplied, this system does not monitor current, though other systems mayhave circuitry in place to do so.

At time t=3, the controller begins driving the motor again at a powerduty cycle of 25% which is a fraction of the target power level basedoff the stored sensitivity profile 50 because braking is active. Duringthis time period, due to the motor being driven, the motor current canbe measured and is determined to be 700 mA.

At time t=4, because the controller 20 has determined at t=3 that thecurrent is decreasing and hence the derived load, the controller appliesthe brake again but at a 15% duty cycle to continue to slow down themotor's speed to 700 RPM. Again, because breaking is occurring, themotor current cannot be read. However, the operator is continuing toreduce the workpiece force and at this point the motor load is 60 N*cm.

At time t=5, the controller 20 begins to drive the motor again but at areduced duty cycle of 12.5% which is half of the previous drive level attime t=3. This drive allows for current measurement which is measured at500 mA. This measured current is a result of a workpiece derived load of50 N*cm. The motor speed for reference is still 700 RPM.

At time t=6, the controller 20 applies breaking again at 15% duty cycleas the current in the previous cycle t=5 was determined to be decreasingfrom the prior measured cycle t=3. This braking causes the speed of themotor to undershoot to a level of 400 RPM. Again, due to this being abraking cycle, the motor current is undetermined. However, the operator12 continues to exert a force on the workpiece 28 which associates to amotor load of 50 N*cm.

At time t=7, the motor speed has continued to decrease to 350 RPM andthe controller 20 continues to drive the motor at a duty cycle of 12.5%of full power. A current measurement is taken from the motor and it ismeasured at 500 mA and a workpiece derived load of 50 N*cm. This is thesame value as measured at time t=5 as the load is now constant.

At time t=8, since the current 95 is substantially constant, thecontroller sets the driving duty cycle at the value determined by thesensitivity profile 50 and the current 95. This increased drive levelthen causes the motor to increase its speed to 450 RPM as it begins tocatch up to the expected steady-state level of 500 RPM.

At time t=9, the operator continues to impart a workpiece load of 50N*cm and the controller measures a motor current of 500 mA which issubstantially the same as previously in time t=8 so the controllercontinues to drive the motor at a 25% duty cycle determined by thesensitivity profile 50 and the current level. The RPM is now indicatedto be 500 RPM and will continue to remain at that speed until theoperator applies more or less force to the workpiece 28.

FIG. 9 is a graph of a normalized approximate material removal rate vs.derived force for an abrasive tool operating at a fixed speed andseveral examples of the tool operating at force responsive speeds havingdifferent sensitivity profiles 50. In this example, the fixed speed 100is set to the max speed for the tool and normalized to “1”. The derivedforce detected at the working surface is the “X-axis value.” Thematerial removal rate (the rate of work in this example) isapproximately the RPM of the working surface times the torque at thephysical working surface axis, as represented by the derived force.Accordingly, the maximum material removal rate (mrr) for any givenderived force within the operating range is mrr profile 100, or thefunction: X*1 for the tool operating at maximum fixed speed. The maximummaterial removal rate for mrr profile 100 occurs when the workpiece ismaximally engaged. The minimum material removal rate for mrr profile 100is 0*1 or zero when the workpiece is not engaged. For the tool operatingat any force responsive speed, the approximate material removal rate isthe derived force “X”, at a consistent point of engagement, times theRPM of the working surface, which is from the sensitivity line. Thus,for mrr profile 102, the approximate material removal rate is labeled asX*X^(0.25) where X^(0.25) is the associated sensitivity RPM. For mrrprofile 104, the approximate material removal rate is labeled asX*X^(0.5). Similarly for approximate mrr profiles 106, 108, 110, theyare labeled as X*X, X*X², and X*X⁴, respectively.

Note that for a given desired material removal rate M1, a derived forceof F1 is measured when operating the tool at a fixed max speed. For allmrr profiles 102, 104, 106, 108, and 110, their sensitivity profilesallow the tool to increase the measured amount of derived force(representing the actual force) necessary to achieve the same desiredmaterial removal rate M1. That is, the derived force F2 for mrr profile102 is greater than F1. Similarly, F3 is greater than F1 and F2, F4 isgreater than F1-F3, F5 is greater than F1-F4, and F6 is greater thanF1-F5. Each of the mrr profiles 102-110 extends the range of force thatcan be used to adjust both the speed of the tool and the desiredmaterial removal rate to achieve Desired MRR M1, thus allowing anoperator to skillfully craft the workpiece with finesse without abruptlyremoving too much material or causing the workpiece to jump or otherwisenot accurately engage as desired on the working surface of the tool.Stated differently, for substantially all of the derived force range,other than the starting zero force and the max derived force endpoints,the material removal rate is less than a respective material removalrate for the tool operating at a fixed max speed.

FIG. 10 is another graph which illustrates the different materialremoval rate ratios between the tool operating at a fixed max speed andwith a couple of force responsive sensitivity profiles that allow thepower tool 10 to have the speed responsive to the derived force. TheX-axis is now a normalized Derived Force 35′ where the max forceavailable is set to “1” and the minimum force is just over “0” or asshown on the graph “>0”. Zero is not shown on the X-axis because theratio is 0/0, zero divided by zero, which is undefined in this case.These force endpoints correspond to a max speed and an initial speed onthe force responsive tool and, specifically for this example, theinitial speed is 5% of the max speed. The Y-axis is a ratio of thematerial removal rate (the rate of work) for the tool operating at aconstant max speed and the tool operating in a force responsive (FR)manner using sensitivity profiles. Here, when the tool is operating at aconstant max speed, the material removal rate follows the mrr profile100 in FIG. 9. When the tool is operating in a force responsive manner,such as mrr profile 106 of FIG. 9, it has a different material removalrate vs. derived force. Plot 120 in FIG. 10 shows the ratio (X*1)/(X*X)of (mrr profile 100)/(mrr profile 106). As the normalized derived force35′ approaches zero force, the mrr profile 106 removes 20 times lessmaterial. As the normalized derived force 35′ approaches “1”, mrrprofile 106 removes the same amount of material as mrr profile 100 dueto the tool operating at the same max speed in each instance. At about45% of the normalized derived force 35′ range, the mrr profile is stillable to remove ½ the material as compared to the tool operating with mrrprofile 100. Thus, a considerable amount of force variance (from 0 to45% of the total work load force) can be used by an operator to finesseand greatly control the rate of work and functional speed of the workingsurface, yet still have more than half the normalized derived forcerange (from 45% to 100%) to operate the tool where fast material removalis still possible. That is, at least 10% of the normalized derived forcerange of the work load force allows for at least a ½ reduction in therate of work (mrr) relative to a rate of work (mrr) at the tool maxspeed 59 at an equivalent work load force. Productivity is increased asthe workpiece no longer would need to be transferred between a firstpower tool and a finishing tool to achieve high rate of work (mrr) andfine finishing of the work, respectively.

Plot 122 in FIG. 10 illustrates another example where the normalizedforce range can be expanded further for finessing the workpiece. In thisexample, the ratio is (X*1)/(X*X²) when using mrr profile 100 and mrrprofile 108 from FIG. 9. Again, as the normalized derived force 35′approaches zero, the tool with mrr profile 108 is removing 1/20^(th) theamount of material as for mrr profile 100 (a constant max speed).However, for the tool with mrr profile 108, an operator can apply aforce range from 0 to 70% before having the tool remove ½ the amount ofmaterial as mrr profile 100. This mrr profile 108 allows the operatorthe ability to remove large amounts of material at the same rate asprofile 100 but also extends the range of control for finessing of aworkpiece or working to exacting standards. For example, a power tool 10for operating on a workpiece 28 includes a motion actuator 14 coupled toa working surface 16 to engage the workpiece 28. A controller 20,coupled to the motion actuator 14, receives a signal 35 representing awork load force the workpiece 28 exerts on the working surface 16. Thecontroller 20 both: a) sets a functional speed of the working surface 16between an initial speed 55 at a first force and a tool max speed 59 ata second force, and b) at all work load forces greater than the firstforce and less than the second force, lowers a rate of work at thefunctional speed relative to a rate of work at the tool max speed 59 atan equivalent workload force. Further, the rate of work at thefunctional speed may be lowered by at least a factor of 2 for at least10% (percent) of a force range between the first force and the secondforce.

FIG. 11 is an example block diagram of a control system 120 that anexisting tool 110 using a working surface 16 can implement with theconcepts described herein. Many existing tools 110, such as an anglegrinder, can run directly from line power input 112 or have a settingsuch that the speed of the existing tool 110 follows the level of theinput line voltage to the tool.

These type of tools are typically built with universal motors or brushedDC motors as motion actuator 14. A universal motor's torque varies withcurrent squared. A brushed DC motor's torque and current have a directrelationship. However, in each case for motion actuator 14 in existingtool 110, the amount of force exerted by an operator 12 on a workpiece28 can be detected and derived by monitoring one or more electricalproperties, such as current, in the power control output 114 supplied tothe existing tool 110. As different tools draw different current levelsand have different torque-current relationships, the controller 20 maybe customized and/or calibrated for various existing tools.

The motion actuator 14 of existing tool 110 actuates a working surface16 which operates on a workpiece 28, either by having an operator 12apply an operator force 30 on the workpiece 28 which transfers force tothe working surface 16 or by having the operator 12 apply anoperator-tool force 21 on the existing tool 110 and the existing tool110 indirectly applying that force on the workpiece 28 via indirect toolforces 23A to the working surface 16 and 23B from the working surface 16to the workpiece 28. The existing tool 110 may include the workingsurface 16, which is configured to engage the workpiece 28. Existingtool 110 may be alternately configured to couple to working surface 16so it can be interchanged as necessary. The existing tool 110 includesmotion actuator 14 that is coupled 37 to the working surface 16.

A controller such as controller 20 is coupled 36 to a power control 116circuit to control the amount of power delivered by the power controloutput 114 to the existing tool 110 and the working surface 16. Thispower control may be done typically by controlling the voltage output,but controlling current and phase, or combinations thereof, are alsopossible. A force detector 18 is coupled to the power control 116circuit via force value 34, and force detector 18 is used to detect oneor more of the current, voltage, power, or phase(s) delivered toexisting tool 110. Force value 34 represents the force, load, orpressure on the working surface 16, which an operator 12 applies to theworkpiece 28 on the working surface 16. The force detector 18 isconfigured to receive the force value 34 and output a signal thatrepresents a derived force 35. The controller 20 may include a centralprocessing unit (CPU) 122 or microcontroller and tangible non-transitorycomputer readable memory 124 having instructions for executing on theCPU 122 to allow the controller 20 to adjust the power control output114 from power control 116 based on the force value 34 via the forcedetector 18. The controller may also be implemented with digital logic,analog circuitry or a combination thereof. The controller 20 may includea sensitivity controller 19 to allow the operator 12 to control withfinesse simultaneously both a rate of work from the workpiece and aspeed of the motion actuator of existing tool 110 based on apredetermined continuous response in sensitivity profile 50 (see FIG. 3and FIGS. 5A & 5B) to the amount of force applied by the operator 12 onthe workpiece 28 at the working surface 16.

The controller 20 may be configured to increase the power to the workingsurface 16 via power control 116 when the controller 20 and/or forcedetector 18 determines an increase in force above a first predeterminedamount and to decrease the power to the working surface 16 when thecontroller 20 and force detector 18 determines a decrease in force abovea second predetermined amount. The controller 20 may also be configuredto maintain the power to the working surface 16 when the force detector18 determines no substantial change in force.

The force detector 18 may be a standardized force detector representinga predetermined force-output function independent of how the amount ofdirect force 30 (or indirect forces 21 and 23A and 23B) the operator 12applies on the workpiece 28 is derived. The force detector 18 maydetermine the operator force applied to the workpiece 28 as force value34 using a voltage sensor, current sensor, power sensor, frequencysensor, phase sensor, or another electrical property sensor orcombinations thereof could be used. Accordingly, as there are manydifferent possible ways to sense or otherwise derive the force theoperator applies to the workpiece, the force detector 18 may convert areceived signal into a standard format so that the controller 20programming does not necessarily need to be updated for different typesof tool implementations, just force detector 18.

Other possibilities to configure controller 20 are possible. Thecontroller 20 may allow for selection of an initial speed as a minimumspeed using an initial speed selector 24 via an initial speed input 39and a max speed using a max speed selector 26 via a max speed input 32.The sensitivity profile 50 (see FIG. 3) applied to the amount of derivedforce on the workpiece at the working surface may be configured to onlyvary in a range between a selected initial speed and a selected maxspeed. However, there may be multiple sensitivity profiles 50 (see FIGS.5A, 5B & 6C) available for an operator to choose from depending onoperator preference and the type of work to be performed on theworkpiece. This selection can be done with a sensitivity selector 22 viaa sensitivity input 38. The sensitivity selector 22 may be configured toselect and apply one of two or more sensitivity profiles (see FIGS. 5A,5B, & 6C) that represent the desired predetermined continuous response50. While the sensitivity profile 50 may represent the relationshipbetween the derived force on the work-piece 28 and observed speed orpower (as a proxy) applied to the motion actuator in existing tool 110,the controller 20 of control system 120 may control the power controloutput 114 to the motion actuator 14 in existing tool 110 in discretesteps over multiple time periods that approximate using the sensitivityprofile 50 as a digital calculation, reference look-up or table, to setthe operating speed of the working surface. The controller's 20 use ofthe sensitivity profile 50 allows any tolerances and other variabilityof the motion actuator 14 in existing tool 110, controller 20, and forcedetector 18 to be compensated for by the finessed control of theoperator 12 as he/she applies their artisan or skilled abilities to theworkpiece 28 or existing tool 110.

In summary, many examples have been described above. The power tool 10and control system 120 with existing tool 110 examples have manyadvantages and increased utility over conventional power tools. Forinstance, the derived force-speed response can be tailored for delicatetool operations such as finessing a workpiece by a skilled artisan toachieve a material removal rate that is more controlled than currentlypossible. Further, the power tool 10 and control system 120 examplesallow for more accurate initial engagement of the workpiece. Thisadvantage allows for improved operator control over the startingalignment of the workpiece with respect to conventional tools such asthe blade of power saws and cutters, drills, and abrading surfaces ofpower sanders and power grinders and other power tools.

Other advantages include a reduced wandering of drill bits on surfaceswhere drilling a pilot hole or center punching is too difficult or nearimpossible to center the drill bit. For instance, as on very hard andsmooth surfaces like metal, the power tool 10 and control system 120examples allow the drill to operate at slow speed over a wide range offorce or pressure applied to the tool to allow the drill bit to form ashallow indentation in the workpiece surface at a desired location torestrain the drill bit from moving laterally.

Likewise, reduced skating or jerking of a hand-held tool or workpiece isnow possible with the power tool 10 and control system 120 examples. Byallowing initial speeds from zero to a slow finite speed at low loads, aworkpiece that engages the tool will not initially encounter a speedhigh enough to create erratic workpiece engagement, or workpiece damage.This advantage allows the operator to grip the workpiece and apply asufficient force or pressure on the workpiece when engaging it to thetool's working surface without sudden unexpected movement of theworkpiece. The operator is able to now align the workpiece withsufficient muscular force and maximal dexterity to control the alignmentof the workpiece with respect to the tool, and the rate of work withhand or other pressure to the workpiece.

While the present invention has been particularly shown and describedwith reference to the foregoing examples, those skilled in the art willunderstand that many variations may be made therein without departingfrom the spirit and scope of the invention as defined in the followingclaims. This description should be understood to include all novel andnon-obvious combinations of elements described herein, and claims may bepresented in this or a later application to any novel and non-obviouscombination of these elements. The foregoing examples are illustrative,and no single feature or element is essential to all possiblecombinations that may be claimed in this or a later application. Wherethe claims recite “a” or “a first” element of the equivalent thereof,such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements.

What is claimed is:
 1. A tool for operating on a workpiece, the toolcomprising: a motion actuator configured to be coupled to a workingsurface to engage the workpiece; a controller coupled to the motionactuator to responsively vary a speed of the motion actuator and anoperating speed of the working surface within the range of an initialspeed and a max speed, and configured to respond to a derived force thatrepresents an amount of force an operator applies between the workpieceand the working surface, wherein the controller is further configured,under both acceleration and deceleration, to allow the operator with anapplied force to manageably change simultaneously both a rate of work onthe workpiece and the operating speed of the working surface accordingto a sensitivity profile expressing a relationship between the derivedamount of force and the operating speed of the working surface.
 2. Thetool of claim 1, further comprising a force detector coupled to thecontroller and configured to output a signal representing the derivedamount of force, wherein the controller is further configured to receivethe signal from the force detector
 3. The tool of claim 2 wherein theforce detector is configured to output a standardized predeterminedforce-output function independent of how the amount of force theoperator applies on the workpiece is derived.
 4. The tool of claim 2wherein the sensitivity profile response allows for variances of themotion actuator, controller, and force detector to be compensated for bythe finesse control of the operator.
 5. The tool of claim 2 wherein thecontroller is configured to increase the operating speed of the workingsurface when the force detector represents an increase in force by afirst predetermined amount and to decrease the operating speed to theworking surface when the force detector represents a decrease in forceby a second predetermined amount.
 6. The tool of claim 5 wherein themotion actuator includes a brake and the controller is configured toapply the brake as needed when the force detector represents a decreasein force by the second predetermined amount.
 7. The tool of claim 6wherein the controller is configured to alternately apply the brake andpower to the motion actuator when a decrease in force applied by theoperator by the second predetermined amount is detected.
 8. The tool ofclaim 1, wherein the controller includes a sensitivity controllerconfigured to implement the sensitivity profile, the sensitivitycontroller coupled to a force detector and the controller is configuredto change the operating speed of the working surface based on apredetermined continuous response profile to the derived amount offorce.
 9. The tool of claim 8 further comprising a sensitivity selectorconfigured to select and apply one of two or more sensitivity profilesthat represent the predetermined continuous response profile.
 10. Thetool of claim 8 where the controller allows for selection of at leastone of the initial speed and the max speed; and the predeterminedcontinuous response profile in the controller is configured to onlyrespond in a range between a selected initial speed and a selected maxspeed.
 11. The tool of claim 1 wherein the controller controls power tothe motion actuator in discrete steps over multiple time periods to setthe operating speed of the working surface.
 12. A method of controllinga power tool, comprising the steps of: deriving a first force applied byan operator to a workpiece onto the working surface during a first timeinterval; setting a first operating speed of a working surface coupledto a motion actuator based on a predetermined continuous responseprofile; deriving a second force applied onto the workpiece to theworking surface of the power tool during a second time interval; whenthe second force is greater than the first force by a firstpredetermined amount, adjusting to a second operating speed based on apredetermined continuous response profile and the second force; when thesecond force is less than the first force by a second predeterminedamount, adjusting to a third operating speed based on the predeterminedcontinuous response profile and the second force; when the second forceis determined to be less than the first force plus the firstpredetermined amount and greater than the first force minus the secondpredetermined amount, adjusting to a fourth operating speed to the powertool based on the predetermined continuous response profile and thesecond force.
 13. The method of claim 12, further comprising the stepof: utilizing a standardized force detector representing a predeterminedforce-output function independent of how the amount of force applied onthe workpiece is derived.
 14. The method of claim 12, further comprisingthe step of: applying a brake during a least a portion of the secondtime interval or a third time interval.
 15. The method of claim 14,further comprising the step of: alternately applying the brake andadjusting power to the motion actuator.
 16. The method of claim 12,further comprising the step of: determining a selection of an initialspeed and a max speed and the predetermined continuous response profileis configured to only respond in a range between a selected initialspeed and a selected max speed.
 17. The method of claim 12, furthercomprising the step of: determining a selection of one of two or moresensitivity profiles that represent the predetermined continuousresponse profiles.
 18. The method of claim 12, wherein the stepsderiving a first force and deriving a second force occur in discretesteps over multiple time intervals.
 19. The method of claim 12 whereinthe predetermined continuous response profile allows tolerances of amotion actuator, a controller, and a force detector to be compensatedfor by the finesse control of the operator.
 20. A method of controllinga power tool, comprising the steps of: deriving a first force applied byan operator during a first time interval from a workpiece onto a workingsurface of the power tool; setting a first power to the power tool;deriving a second force applied by an operator during a second timeinterval from the workpiece onto the working surface of the power tool;when the second force is greater than the first force by a firstpredetermined amount, adjusting a second power to the power tool basedon a sensitivity profile and the second force; when the second force isless than the first force by a second predetermined amount, adjusting athird power to the power tool based on the sensitivity profile and thesecond force; and when the second force is determined to be less thanthe first force plus the first predetermined amount and greater than thefirst force minus the second predetermined amount, applying a fourthpower to the power tool based on the sensitivity profile and the secondforce.
 21. A control system for a tool to operate on a workpiece, thecontrol system comprising: a controller configured to couple to a motionactuator to responsively vary the amount of power delivered by themotion actuator to a working surface of the tool, and further configuredto couple to a force detector configured to output a signal representinga derived amount of force an operator applies between the workpiece andthe working surface, wherein the controller is further configured, underboth acceleration and deceleration, to receive the signal from the forcedetector and allow the operator with an applied force to manageablychange simultaneously both a rate of work on the workpiece and theoperating speed of the working surface according to a sensitivityprofile expressing a relationship between the derived amount of forceand the operating speed of the working surface.
 22. A tangiblenon-transitory computer readable medium for executing instructions on acomputer, the medium including routines to: respond to a derived forcerepresenting a first force applied by an operator from a workpiece ontothe working surface during a first time interval; set a first operatingspeed of a working surface coupled to a motion actuator; respond to aderived force representing a second force applied from the workpieceonto the working surface of the power tool during a second timeinterval; when the second derived force is greater than the firstderived force by a first predetermined amount, adjust a second operatingspeed based on a predetermined continuous response profile and thesecond force; when the second derived force is less than the firstderived force by a second predetermined amount, adjust a third operatingspeed based on the predetermined continuous response profile and thesecond force; when the second derived force is determined to be lessthan the first derived force plus the first predetermined amount andgreater than the first force minus the second predetermined amount,apply a fourth operating speed to the power tool based on thepredetermined continuous response profile and the second force.
 23. Apower tool for operating on a workpiece, the tool comprising: a motionactuator coupled to a working surface to engage the workpiece; acontroller coupled to the motion actuator and configured to receive asignal representing a work load force the workpiece exerts on theworking surface, and the controller is further configured to both: a)set a functional speed of the working surface between an initial speedat a first force and a tool max speed at a second force, and b) at allwork load forces greater than the first force and less than the secondforce, lower a first rate of work at the functional speed relative to asecond rate of work at the tool max speed at an equivalent work loadforce.
 24. The tool of claim 23, wherein the first rate of work at thefunctional speed is lowered by at least a factor of 2 for at least 10percent of a force range between the first force and the second force.